1. Field of the Invention
The present invention relates to magnetic induction heating devices, systems, and methods. More particularly, the invention relates to a heat-retentive, induction-heatable body that may be embedded or inserted in stadium seats, food delivery bags or trays, or other objects to heat or warm the objects. The invention also relates to an RFID-based induction heating/vending system that may be used to quickly and easily heat and vend stadium seats, food delivery items or other objects and to then efficiently collect the objects from customers after use.
2. Description of the Prior Art
It is desirable to keep hot foods, such as pizza, warm during delivery. One method of doing so is to insert or incorporate a heat-retentive body into a food-holding container such as a pizza delivery bag to maintain the temperature of the food item during delivery. Examples of such systems and methods are disclosed in U.S. Pat. No. 6,232,585 (the ""585 patent) and U.S. Pat. No. 6,320,169 (the ""169 patent), both owned by the assignee of the present application and incorporated into the present application by reference. Specifically, these patents disclose temperature self-regulating food delivery systems and magnetic induction heating methods that utilize a magnetic induction heater and a corresponding induction-heatable body to maintain the temperature of a food item or other object during delivery.
Although the systems and methods disclosed in the ""585 and ""169 patents are far superior to prior art systems and methods for keeping food and other items warm, they suffer from several limitations which limit their utility. For example, the induction-heatable bodies disclosed in these patents cannot be heated quickly, especially to a high temperature. Induction-heatable bodies made of high cost, fine ferromagnetic materials and can be heated more quickly than those made of lower grade ferromagnetic materials, but such devices are relatively costly and heavy and thus impractical for many applications such as portable, cost-sensitive food delivery systems. Many prior art induction-heatable bodies also often develop xe2x80x9chot spotsxe2x80x9d when heated by a heating source having an uneven magnetic field distribution such as is provided by typical flat pancake spiral induction heating coils.
Prior art food delivery systems which incorporate induction-heatable bodies also suffer from several distinct disadvantages. For example, such systems are especially configured for holding and warming pizza, but not other types of food. Although pizza likely constitutes the largest percentage of delivered food items in the U.S., it is believed that consumers would accept and desire many other types of delivered food items if such food items could be kept warm during delivery. Specifically, it is believed that consumers would readily request the delivery of sandwiches and french fries such as those sold by the McDonald""s Corporation if food delivery systems existed for maintaining the temperature of these food items during delivery.
It is also often desirable to heat objects other than food items. For example, portable, heatable seat cushions (thermal seats) are popular for use by consumers to stay warm and comfortable while seated in conventional stadium or bleacher seats during outdoor sporting events, concerts and other similar events. Several such thermal seats are disclosed in U.S. Pat. Nos. 5,545,198; 5,700,284; 5,300,105; and 5,357,693, which generally describe seat cushions including a removable envelope enclosing a fluid which can be heated in a microwave oven. A primary disadvantage of these types of thermal seats is that they do not retain heat long and therefore are unsuitable for use during many longer activities such as concerts and sporting events.
Moreover, because the fluid envelopes must be heated in microwaves, it is difficult to heat and commercially rent a large number of these types of thermal seats to customers at sporting events or concerts. The commercial rental of thermal seats has also been impractical because of the difficulties in collecting the seats back from customers after they have been used. Currently, thermal seats must be heated, vended and recollected manually, requiring too much labor to be cost-effective.
The present invention solves the above described problems and provides a distinct advance in the art of heat-retentive induction-heatable bodies, food delivery systems, and systems for vending and recollecting thermal seats.
One embodiment of the present invention is an induction heatable body that quickly heats to a desired temperature, retains heat long enough to be used in almost any application, and develops no xe2x80x9chot spots,xe2x80x9d even when heated by a heating source having an uneven magnetic field distribution. Moreover, the induction-heatable body of the present invention achieves the foregoing while remaining relatively lightweight, inexpensive and easy to manufacture.
A preferred embodiment of the induction-heatable body broadly includes a plurality of induction-heatable layers each sandwiched between alternating layers of heat retentive material. The induction-heatable layers preferably consist of sheets of graphite material that can be inductively heated at magnetic field frequencies between 20 and 50 kHz. The heat-retentive layers preferably consist of solid-to-solid phase change material such as radiation cross-linked polyethylene.
The skin depth of each of the induction-heatable layers is large enough to permit complete and substantially simultaneous inductive heating of all of the layers when the induction-heatable body is placed on or in the vicinity of an induction heating coil. This allows a great amount of surface area to be simultaneously heated so that the induction-heatable body is quickly heated to a desired temperature by a typical induction heating coil and retains the heat for a long period of time. The alternating layers of induction-heatable material and heat-retentive material quickly and uniformly conduct heat so that any xe2x80x9chot spotsxe2x80x9d created during heating of the induction body are quickly eliminated.
Another embodiment of the present invention is a food delivery assembly uniquely adapted and configured for maintaining the temperature of sandwiches, french fries, and other related food items such as those sold by the McDonald""s Corporation. The food delivery assembly broadly includes a magnetic induction heater, a food container, and a delivery bag for carrying and insulating the food container. The magnetic induction heater operates under the same principles as disclosed in the ""585 and ""169 patents but is specially sized and configured for heating the food container of the present invention. The preferred magnetic induction heater includes an L-shaped base or body with an induction heating coil positioned in or on each leg of the body. The magnetic induction coils are controlled by a common control source and are coupled with an RFID reader/writer.
The food container preferably includes an outer, open-topped box, an inner open-topped box that fits within the outer box, a plurality of divider walls that fit within the inner box to subdivide it for receiving several separate food items, and a lid that fits over the open top of the inner box to substantially seal the food container and retain heat therein. The food container may be sized and configured for holding any types of food items such as sandwiches and french fries sold by the McDonald""s Corporation. Two induction-heatable cores are positioned on two exterior walls of the inner box and are sized and oriented so as to be positioned adjacent the induction heating coils of the magnetic induction heater when the food container is placed on the heater. The induction-heatable cores are preferably substantially identical to the induction-heatable body described above. An RFID tag and thermal switch are also coupled with the induction-heatable cores and operate substantially the same as described in the ""585 and ""169 patents.
The delivery bag is preferably formed of lightweight, flexible, insulative material and includes a compartment for receiving and insulating the food container. The delivery bag may also include a separate compartment for receiving and insulating cold food items such as soft drinks.
Another embodiment of the present invention is an RFID-based induction heating/vending system for quickly and efficiently heating, vending, and recollecting stadium seats or other objects used during sporting events, concerts, and similar events. The system broadly includes any number of thermal seats each including an induction-heatable body such as the one described above; a charging/vending station for heating and vending the seats; a self-serve warming station that may be used by consumers to reheat their seats; and a check-out station in which consumers may deposit their thermal seats after an event.
The thermal seats are configured for placement on conventional stadium or bleacher seats for increasing the comfort and warmth of the seats. Along with an induction-heatable body, each thermal seat includes one or more layers of solid state phase change material designed to store a vast amount of thermal energy. The thermal seats can be inductively heated on an RFID induction heater and each contains an RFID tag so as to allow it to be temperature regulated as per the ""169 and ""585 patents. These tags may be linked to a thermal switch, also as described in the ""169 patent. The RFID tags also store customer information, such as credit card numbers, and the time and date seats were given to customers. This information is stored on an RFID tag of a seat while it is heated by the induction heaters of the charging/vending station as described below.
The charging/vending station includes one or more induction heaters as described in the ""585 patent, an RFID reader/writer associated with each heater, and a credit card reader, which may be connected to more than one induction heater with a microprocessor controlling the flow of information. When it is desired to vend a seat to a customer, the seat is placed on top of one of the induction heaters and the customer""s credit card is scanned. As the credit card is scanned, the information on the card is sent to the RFID reader/writer associated with the induction heater and then written to the RFID tag of the thermal seat being vended. At about the same time, the RFID reader/writer reads and recognizes the class of object code on the RFID tag embedded in the thermal seat and executes a specific heating algorithm designed to efficiently bring the seat to a pre-selected temperature and maintain it there without input from the vendor. The charging/vending station also preferably includes a simple control system such as a red light to indicate charging and a green light to indicate that charging is complete so that a seat may be removed from the heater and vended to a customer.
The self-serve warming station is similar to the charging/vending station but lacks the cash register and card reader. The warming station includes one or more induction heaters and an RFID reader/writer associated with each heater. The warming station allows customers to reheat their seat should the seats not stay hot during the entire duration of an event. Furthermore, a customer who has rented a thermal seat can use the self-serve station to initially heat his or her thermal seat if there is a line at the charging/vending station.
A vendor or customer may also use the charging/vending station or the self-serve warming station to initially heat or reheat food delivery containers or other devices during an event. Many self-serve warming stations could be placed at strategic locations around a stadium or other venue to allow easy access for customers or vendors. Simple instructions at each station would allow customers and vendors to easily and safely heat their thermal seats, food delivery containers or other items without assistance.
The check-out station includes a substantially enclosed housing having one or more openings or xe2x80x9cchutesxe2x80x9d into which thermal seats may be placed so as to irretrievably fall into the housing. An RFID antenna is positioned adjacent each chute and is in communication with an RFID reader/writer and microcontroller control unit. The RFID antenna reads the RFID tag of a thermal seat as it is deposited in the housing. The RFID reader/writer and microcontroller control unit communicate with a receipt printer to dispense a receipt shortly after a seat has been placed into the chute. The microcontroller control unit also stores transaction information, including the time and date each seat was returned, so that the information can be immediately or subsequently retrieved either through a direct cable connection, a modem, or a wireless modem. The transaction information can then be compiled with that of other check-out stations so as to effectively monitor the status of all vended thermal seats.
The control unit of the check-out station preferably has a user interface similar to those found in other automated vending systems such as self-serve gas pumps. The user interface instructs a customer to place a thermal seat into the chute and to then take his or her receipt. The simple operation of the check-out stations allows a large number of thermal seats to be quickly returned without intervention by paid staff members.
The heating/vending system of the present invention provides numerous advantages not found in the prior art. For example, the thermal seats can be quickly, easily and automatically heated to a predetermined temperature on an RFID-equipped induction heater. The RFID tag embedded in each seat can receive and store customer information during the vending process so as to identify the customer when the seat is returned.
The charging/vending station allows the thermal seats to be initially heated by a vendor and simultaneously loaded with the customer""s identification information at the time of vending. The check-out station may then be used to return seats, identify a returned seat, identify the customer who rented it, identify the time at which the seat was returned, give the customer a receipt immediately showing his charges, and store the transaction information for immediate or future download to a central data base.
The self-serve warming station allows customers and vendors to easily reheat seats during an event. Advantageously, the warming station can bring a seat back to its pre-determined temperature without any input from the consumer.
The charging/vending station and self-serve warming station may also be used to heat other objects such as food delivery bags and trays. Consumers could use these bags and trays to keep their food warm during sporting events, concerts, and other events and then return the bags or trays to the check-out station as described above.